Catalytic cracking is a petroleum refining process that is applied commercially on a very large scale. A majority of the refinery petroleum products are produced using the fluid catalytic cracking (FCC) process. An FCC process typically involves the cracking of heavy hydrocarbon feedstocks to lighter products by contacting the feedstock in a cyclic catalyst recirculation cracking process with a circulating fluidizable catalytic cracking catalyst inventory consisting of particles having a mean particle size ranging from about 20 μm to about 150 μm, preferably from about 50 μm to about 100 μm.
The catalytic cracking occurs when relatively high molecular weight hydrocarbon feedstocks are converted into lighter products by reactions taking place at elevated temperature in the presence of a catalyst, with the majority of the conversion or cracking occurring in the vapor phase. The feedstock is converted into gasoline, distillate and other liquid cracked products as well as lighter gaseous cracked products of four or less carbon atoms per molecule. The gas partly consists of olefins and partly of saturated hydrocarbons. Bottoms and coke are also produced.
Generally, the product distribution obtainable from modern catalyst cracking units, in particularly, the fluid catalytic cracking (FCC) units, is acceptable. However, many refiners desire improved catalytic cracking methods or processes which increase the volume of light olefins products as well as the volume and octane number of gasoline products. It is also desirable to produce the lowest bottoms at a constant or decreased coke level.
FCC catalysts normally consist of a range of extremely small spherical particles. Commercial grades normally have average particle sizes ranging from about 20 μm to 150 μm, preferably from about 50 μm to about 100 μm. The cracking catalysts are comprised of a number of components, each of which is designed to enhance the overall performance of the catalyst. FCC catalysts are generally composed of catalytically active zeolite, active matrix, clay and binder with all of the components incorporated into a single particle. Alternatively, the catalysts are comprised of blends of the individual particles having different functions.
FCC catalysts containing rare earth exchanged zeolites are in wide commercial use and their general technical properties are widely known. See Fluid Catalytic Cracking with Zeolite Catalysts, Venuto and Habib, 1979 Marcel Dekker, In., pp. 30-46. Further, FCC catalysts comprising Y-type zeolite exchanged with rare earths have been disclosed in numerous patents including U.S. Pat. Nos. 3,436,357 and 3,930,987.
U.S. Pat. No. 4,405,443, discloses that zeolite exchanged with rare earth, then mixed with yttrium and an inorganic oxide provide an absorbent for sulfur oxides.
U.S. Pat. No. 4,793,827 discloses a hydrocarbon cracking catalyst which comprises rare earth exchanged Y-type zeolite which has been ion exchanged to enhance the yttrium content of the catalyst.
U.S. Pat. No. 5,908,547 discloses yttrium containing zeolite Y-type catalysts which are essentially free of rare earth ions.